The present invention relates to a radar device used in motor vehicles.
Radar devices may be used in motor vehicles to measure the distance from, and the speed relative to, a motor vehicle or an obstacle. During the measurement it must be ensured that only reflections from objects located on the same lane as the vehicle to be measured are considered. Reflections from guardrails, traffic signs, and the like must not be taken into account. To accomplish this, a so-called "electronic road channel" is formed, and only reflections of objects located in this electronic road channel are evaluated.
A radar device generating such an electronic road channel is known from German Published Application (DT-OS) No. 2,327,186. In the radar device described there, two antennas with overlapping radiation patterns radiate rf signals of different frequency. The electronic road channel is equal to the overlap area of the two radiation lobes. The signals of different frequency reflected from an object located with this area, which are received by the two antennas and fed to two receivers, have approximately equal amplitudes. Distance and relative speed are measured only when this condition (approx. equal amplitudes) is satisfied.